The concentration of glucose in blood is important in clinical tests for diagnosing diabetes mellitus and in controlling blood-sugar of individuals having diabetes mellitus. Blood glucose may be measured using an enzyme having specificity to glucose such as, for example, glucose oxidase (GOx).
GOx has been isolated from various kinds of strains and it has been suggested that glucose may be analyzed using such enzymes. GOx is a flavin adenine dinucleotide (FAD)-dependent enzyme that catalyzes a reaction where glucose is oxidized to generate gluconolactone, thereby generating the reduced form of FAD, FADH2. FADH2, in turn, transmits electrons to an electron acceptor and is converted back to its oxidized form. In the presence of oxygen, FADH2 preferentially transmits electrons to oxygen molecules rather than to artificial electron acceptors (also referred to as mediators or electron mediators). Thus, when glucose is assayed by GOx with mediators, the assay results will be greatly affected by the dissolved oxygen level in the reaction system. Such a disadvantage will be particularly noted in clinical tests of blood samples by a point-of-care testing device utilizing an artificial electron acceptor. Therefore, enzymes used for enzyme biosensor test strips employing artificial electron mediators desirably have low activity toward oxygen.
For the foregoing reason, there is a need for an enzyme, in particular, a GOx having an activity that is less affected by the dissolved oxygen level.